Aging is a complex biological process characterized by a gradual but persistent decline in biochemical, physiological and metabolic function of many cells, tissues and organs. Mitochondrial abnormalities have been implicated in the etiology of age-related diseases. Mitochondria contain their own genome (mtDNA) and it has been proposed that mtDNA mutations in somatic tissues accumulate with age, causing a decline in mitochondrial function, and subsequently, age-related diseases and aging itself. In contrast, female germ line (oocyte) mtDNA largely evades mutagenesis and is preserved and replicated with minimal damage. The objective of this proposal is to test the hypothesis that age-related mitochondrial erosion in somatic cells is associated with mtDNA mutations, which in turn adversely affects the developmental competence of iPSCs derived from these cells. Therefore, complete replacement of mutated somatic cell mtDNA is critical for resetting the full developmental competence and therapeutic potential of human iPSCs. We propose to evaluate the effect of aged mitochondria and mutated mtDNA in iPSCs on development and aging in a mouse model, using the definitive chimera assay. To meet our objective, three Specific Aims have been designed. In Aim 1, we will generate genetically identical iPSC lines carrying old and ntESCs with pristine young oocyte mitochondria. In Aim 2, we will define stem cells by genetic, cytogenetic, epigenetic, transcriptional and metabolic profiling. In Aim 3, we will study the development and aging of chimeric offspring generated from stem cells. When completed, this project will provide the direct experimental proof that accumulation of damage and loss of mitochondrial genome integrity plays a central role in the aging process. We will also determine whether the age related mitochondrial erosion in somatic cells affects the developmental potential of experimental PSCs.